Study On The Defects Regulation In Transition Metal Oxides And Sulfides Under Ballmilling And Their Electrocatalytic Oxygen Evolution Reaction

Environmental pollution caused by the massive use of fossil energy has become one of the major problems facing society today.Therefore,clean energy technology has attracted extensive research interest.Among the emerging clean energy technologies,such as electrocatalytic water splitting,etc.,have attracted much attention due to their advantages of obtaining high-purity hydrogen which serve as an important carrier of clean energy.These clean energy technologies are mainly composed of electrocatalytic hydrogen evolution reaction(HER),electrocatalytic oxygen evolution reaction(OER)and other basic electrochemical reactions.These electrocatalytic reaction usually accompany with high reaction energy barrier and sluggish reaction dynamics.Thus,the development of highly active,high stability and inexpensive catalysts is crucial to the development of corresponding clean energy technologies and device.Among oxygen evolution catalysts,transition metal oxides,especially perovskite oxides have rich element composition and high structural flexibility,which has become one of the ideal alternatives electrocatalyst materials.However,how to design and construct oxygen evolution catalytic materials with high activity is still a huge challenge.To achieve the design and synthesis of high-performance catalysts,we need to deeper understand the influence of material intrinsic structure on the catalytic process(including catalytic activity and catalytic mechanism,etc.).In this paper,based on the summary and analysis of relevant research,we expected to explore an efficient and universal material structure regulation method.We selected the defect structure as the research object.Then we study the correlation between defect structure(including defect content,surface defect aggregation,bulk diffusion behavior of defect and defect form)and catalysts'oxygen evolution activity/oxygen evolution mechanism.We further develop the activity descriptors for oxygen evolution process based on related defect structure parameters.By combining the above research with theoretical calculation and structural characterization,we have carried out an in-depth study on the origin of catalytic activity and reaction mechanism.These studies provide theoretical and experimental guidance for the synthesis and application of electrocatalysts.Based on the above analysis,this paper developed a mechanochemical method based on ballmilling process and realized the quantitative and controllable construction of oxygen defects in perovskite oxide Lax Sr1-x Co O3-?.The linear correlation between ballmilling time and oxygen defect content was established,which proved the universality and expansibility of this method.Then,through the oxygen evolution reaction characterization,three OER mechanism shift modes(AEM-LOM,LOM-AEM,AEM-LOM-AEM)associated with oxygen defects were found in this paper.According to the different catalytic mechanisms,the volcano-type relationship between the total oxygen defect contents and OER activity was further established under the AEM and LOM,respectively.The intrinsic activity limitation effect of high concentration oxygen defect on OER activity was also observed.Finally,a unified OER process model of perovskite oxide associated with oxygen defects was proposed and established.Based on above results,the control parameter of the system pressure in ballmilling process was further developed.The controllable construction of surface and bulk oxygen defects was realized in the perovskite oxide Pr0.5Ba0.5Co O3-?.These results expanding the ability of mechanochemical method to regulate the structure of oxygen defects.The formation mechanism of oxygen defects under mechanical force is deeper studied.In addition,through the characterization of the oxygen evolution process,the structure-activity relationship between the surface oxygen defect content parameters,the total oxygen defect content parameters and the corresponding oxygen defect diffusion behavior from surface to bulk phase were established.Besides the OER activity and mechanism related to oxygen defects were further clarified.Next,based on the understanding of the formation mechanism and diffusion behavior of oxygen defects under mechanical force,the surface content of doped sulfur and its bulk phase diffusion behavior in perovskite oxide Pr0.5Ba0.5Co O3-?S0.1 were also controlled.The structure model Pr0.5Ba0.5Co O3-?S0.1 with different sulfur/oxygen defect concentration gradients was constructed,and the OER activity/mechanism of materials were studied from two new perspectives:the interaction between oxygen defect structure and S^2-and the bulk concentration distribution of oxygen defect/S^2-in the material.It was proved that the sulfur doping strategy can significantly promote the OER activity of the materials.At the same time,the mechanism of oxygen defect formation under mechanical force was further improved and verified,and the regulation methods and ideas of oxygen defect structure were enriched.Finally,the ballmilling process inevitably to damage in material morphology,this paper preliminary explored the mechanochemical method based on ultrasonic oscillation process,which avoided the damage to material morphology caused by ballmilling and extended the application of mechanochemical method in the control of catalyst defect structure.Fe Co Sx-PBA heterostructure with abundant amorphous defects was successfully constructed by ultrasonic processing.The intrinsic electron structure of Co site was optimized by the doping of heterogeneous ions(Fe²⁺and S^2-),and the Fe Co Sx-PBA heterogeneous interface enhanced the electron transfer ability of PBA,inhibit the over-adsorption of OH on the catalytic active site,and realize the efficient OER process.At the same time,the Fe Co Sx-PBA heterointerface on the surface also provided protection for PBA,and significantly enhanced the catalytic stability of OER.In addition,Fe Co Sx-PBA heterostructure material can be used as a high-performance cathode catalyst to drive flexible solid aluminum-air batteries with excellent flexibility and stretchability.